A 72-year-old man with known benign prostatic hyperplasia (BPH) treated with tamsulosin presents with worsening lower urinary tract symptoms (LUTS), including nocturia x4, hesitancy, and a sensation of incomplete emptying. His International Prostate Symptom Score (IPSS) is 22 (severe). A recent PSA is 2.5 ng/mL and DRE reveals a moderately enlarged, smooth prostate. According to NICE CG97, what is the most appropriate next step in management if conservative measures and tamsulosin are insufficient?